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Nested Chinese Restaurant Process

In the Nested Chinese Restaurant Process (nCRP), each table refers to another restaurant that represents a lower-level category:

(define top-level-category  (DPmem 1.0 gensym))

(define subordinate-category
  (DPmem 1.0
         (lambda (parent-category)
           (pair (gensym) parent-category))))

(define (sample-category) (subordinate-category (top-level-category)))

(repeat 10 sample-category)

We can use these nested categories to generate observations:

(define possible-observations '(a b c d e f g))

(define top-level-category  (DPmem 1.0 gensym))

(define top-level-category->parameters
  (mem 
    (lambda (cat) 
      (dirichlet (make-list (length possible-observations) 1.0)))))
    
(define subordinate-category
  (DPmem 1.0
         (lambda (parent-category)
           (pair (gensym) parent-category))))

(define subordinate-category->parameters
  (mem  
    (lambda (cat) 
      (dirichlet (top-level-category->parameters (rest cat))))))
    
(define (sample-category) 
  (subordinate-category (top-level-category)))

(define (sample-observation) 
  (multinomial possible-observations 
               (subordinate-category->parameters (sample-category))))

(repeat 10 sample-observation)

References: